>Sunscreen Pollution

By Craig Downs, Ph.D.

>A serious and increasingly clear threat to coral

>Fortunately, demand by concerned consumers is leading to increased availability of less harmful sunscreens.

>Some effects of marine pollution are visible, such as the plastic garbage that often litters reefs and beaches. Other effects are similarly obvious, such as the brimstone stench of a nearshore dead zone caused by sewage and fertilizer runoff. Unfortunately, marine pollution goes even further than most people can easily witness, and these less-apparent aspects of pollution have elusive but far-reaching consequences.

>I first came to understand the significance of sunscreen lotion in marine pollution during an investigation into declining coral reefs in the U.S. Virgin Islands. A local resident complained to my investigative team about an oily, iridescent sheen on the surface of the water that lingered after the mass of tourists had gone home; it was supposedly caused by sunscreen washing off the swimmers. "Swimmer pollution" threatens coral reefs across the world, from the Gulf of Aqaba in the Red Sea to the shores of Playa Hermosa, Costa Rica, and almost everywhere in the Caribbean. Anywhere humans get into the water on or near a reef is a potential avenue for contamination.

>Besides washing off swimmers' skin and into the water, sunscreen can get into the sea by other means. Many sunscreen ingredients are readily absorbed through the skin. Oxybenzone, one of the most common ultraviolet-blocking chemicals in sunscreen, for example, can be detected in urine within 30 minutes of application. When you flush the toilet or wash off sunscreen in the shower, chemicals from the lotion enter the sewer. For towns near coral reefs and without sophisticated sewage treatment and management systems, this pollution is rather inevitable. (There is an etymological argument that the word "sewer" comes from the old English word "sea ward," in which household and municipal waste was channeled out of villages and towns toward the sea or other bodies of water.) Any coral reef near significant human habitation is potentially vulnerable to a plume of pollution.

>Sunscreen lotions do not threaten every single coral reef in the world. Sunscreen and other personal care products, however, do threaten the coral reefs that are most important to people — those that are focal points of tourism as well as fringing reefs that are critical for protecting coasts from erosion. And they threaten the capacity of local subsistence fisherman to access the abundance of food that healthy nearshore reefs once provided. Not only does intense sunscreen pollution threaten the survival of these reefs, but it also can prevent the recovery and restoration of already-degraded reefs.

>Ecotoxicology of Sunscreen Lotions and their Ingredients

>In October 2015 my colleagues and I examined the toxicological effects of oxybenzone on coral larvae.1 We found that oxybenzone induces coral bleaching by lowering the temperature at which corals will bleach when exposed to prolonged heat stress. We also showed that oxybenzone is genotoxic, meaning that it damages coral DNA as well as induces severe and lethal deformities. Most alarming, we determined that oxybenzone also acts as an endocrine disruptor, causing the coral larvae to inappropriately encase itself in its own stony skeleton — at a time in its development when it should not even have a skeleton.

>Our research demonstrated that these pathologies can occur at concentrations as low as 62 parts per trillion. For perspective, beaches in Hawaii have oxybenzone levels higher than 700 parts per trillion early in the morning before swimmers even arrive. Other emerging research is showing that oxybenzone concentrations on nearshore reefs around the world are commonly between 100 parts per trillion and 100 parts per billion — well within the range of being a significant environmental threat.

>Oxybenzone is toxic to more than just corals. It's toxic to algae, sea urchins, fish and mammals. It inhibits embryonic development in sea urchins. It can result in gender shifts in fish, in which male fish take on female attributes, while females have reduced egg production and embryo hatchings. In mammals it has been demonstrated to be a potential mutagen and to exhibit procarcinogenic activity. Studies in both mice and rats showed that exposure to oxybenzone increases liver and kidney weights, reduces immunity, increases uterine weights in juveniles and reduces fertility. In recent studies, human couples whose urine contained higher concentrations of benzophenones had a harder time getting pregnant, while men with higher concentrations had higher levels of diseased sperm. Both dolphin and human mothers can transfer oxybenzone to their infants via breastmilk.

>Oxybenzone and many other common sunscreen ingredients are now>known to damage corals, even in extremely low concentrations.

>There are a host of other chemicals in sunscreen that are potentially toxic to coral reefs, some of which — including methoxycinnamate and camphors — are on the International Chemical Secretariat's SIN (Substitute it Now) list based on their activity as endocrine disruptors to humans and wildlife. Noncoated nanoparticles (less than 35 nanometers in diameter) of zinc oxide and titanium dioxide (referred to as "mineral-based" sunscreens) can be toxic to corals, fish and other reef organisms. Their toxicity arises from both their miniscule size and their interaction with cells, as well as the fact that they cause oxidative stress in sunlight (i.e., they too can cause coral bleaching). Non-nanotized (commercial designation above 150 nanometers in diameter) coated zinc oxide and titanium dioxide don't readily exhibit acute toxicities. Nanoplastic ultraviolet (UV) absorbers, which commonly have diameters of around 350 nanometers, are also not necessarily toxic to the marine environment, though their nanotized property may be a cause for concern.

>An "organic" certification doesn't mean a sunscreen is safe for the environment. A number of plant-based oils can be toxic to reef organisms, especially arthropods. For example, neem, eucalyptus and lavender oils, which are used in some organic sunscreens, also have applications as insect repellents or insecticides, suggesting they may also have increased relative toxicity to invertebrates. Other ingredients such as beeswax can be contaminated with a variety of industrial fungicides and insecticides. Organic ingredients, or any ingredient in a product, should be subjected to toxicological testing.

>Silicone polymers, cyclic siloxanes (e.g., octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane) and other alternatives to oils warrant some concern. These organosilicon compounds are not biodegradable and can bioaccumulate in aquatic and marine organisms, including edible fish. Many sunscreen lotions also contain preservatives, which a growing body of evidence shows are an environmental threat. Parabens are preservatives that inhibit fungal and bacterial growth. At lower concentrations they can act as pheromone and endocrine disruptors, while at higher concentrations they can be acutely toxic to invertebrates. Another preservative, phenoxyethanol, was originally used as an insecticide and an insect repellant, and it can be toxic at low concentrations to invertebrates from shrimp to sea urchins. It is still used as a mass anesthetic for fish in some aquaculture operations.

>We have evidence that many of these ingredients contaminate marine and coastal environments, but our general lack of societal inquiry into their toxicities leaves us with little ability to accurately assess whether they pose a clear and present danger to marine habitats.

>Implications and Solutions

>There is no single, definitive solution to the problem of sunscreen pollution, but a diversity of approaches can be implemented to various effects. All will require further research to determine which ingredients are safe and which pose a realistic threat to marine ecosystems. These approaches also depend on adequate communication of the data to consumers, manufacturers, regulators and other stakeholders. It should be noted that none of these mitigation options require that sunscreen not be used. Sun protection is a significant public health issue, and sunscreens play an important role in the management of this risk.

>One approach is to ban the use of products that contain threatening ingredients in areas where coral reefs are most susceptible to exposure. This type of regulatory policy has been in place for almost 10 years in Mexico's ecoreserves, including Xcaret and Xel-Há. This sort of policy might be the easiest and most cost-effective approach, at least in areas crucial for active reef conservation and restoration, such as coral reef nurseries.

>A second approach involves a public relations campaign, to be implemented in coral reef managed areas such as marine parks and sanctuaries, that informs visitors and locals about the environmental impact of sunscreen pollution and asks them to use suncare products without threatening ingredients. The best current example of this strategy is the U.S. National Park Service's campaign to "Protect Yourself, Protect the Reef."

>I've spoken with a number of dive shop and resort operators about designing and implementing a similar public relations campaign. Many of these businesses promote education and offer a selection of suncare products that are free of the toxic ingredients listed by Mexico's ecoparks or the website MarineSafe.org. Some resorts and dive shops are even proposing to offer coral "safe" sunscreen for free to their guests, although the lack of toxicological data showing what is safe and what isn't is the critical obstacle for any such campaign.

>A third strategy is to convince people to reduce the amount of sunscreen they use. Applying lotion to only the neck, face, feet and backs of hands can reduce sunscreen loads into the water by 90 percent. Sun clothes designed to reduce UV exposure have evolved tremendously in the past 10 years in both fashion and utility. Gone are the days of tight-fitting rashguards or jumpsuits that are a pain to put on and take off, especially when wet; there are now clothes that are comfortable and well suited to the water, the beach and the cafe.

>A fourth option requires consumers to demand innovation from manufacturers regarding the formulation of their products. We are at a juncture in which industry can either demonstrate leadership by developing environmentally sustainable new products that are popular with consumers or dig in its heels, refusing to adapt and suffering economic and reputational consequences. The successful rise of several environmentally conscious companies demonstrates the influence of consumers who demand more sustainable products.

>Whatever we choose to do moving forward, we must remember that the best way to keep marketing honest is for the consumer to demand attention to rigorous and unbiased science from both industry and government — the institutions with the power to inform manufacturers and consumers about which ingredients are gentler to marine ecosystems. Scientific data generated by industry alone is often viewed with suspicion and distrust, with ample historical justification. The relevant science should be conducted by financially neutral parties that follow standardized, validated testing protocols. Governments can play a pivotal role by encouraging third-party testing, standardizing methodologies and moderating dialogue among all interested parties. As with many marine environmental issues, divers are uniquely positioned to both lead by example and benefit from healthier and more vibrant reefs.